1. Field of the Invention
The present invention generally relates to a gold finger of a circuit board and fabrication method thereof, and more particularly, to a gold finger of a circuit board having better tear resistance and fabrication method thereof.
2. Description of Related Art
The main function of a circuit board is to provide connecting circuits between devices. Furthermore, as electronic apparatus becomes increasingly sophisticated and includes more and more devices, the circuits and devices on the circuit board get denser and denser. To connect a circuit board with a motherboard, a connector commonly called ‘gold finger’ is used. The gold finger is normally fabricated using a material such as gold or tin.
Using a Dual In-line Memory Module (DIMM) circuit board as an example, a front view of the conventional DIMM type circuit board is shown in FIG. 1A. As shown in FIG. 1A, the conventional DIMM type circuit board 100 includes a random access memory chip area 102 and a plurality of gold finger 104 leads.
FIG. 1B is a magnified view of area B in FIG. 1A. As shown in FIG. 1B, each of the gold finger 104 leads of the DIMM type circuit board normally includes a gold finger body 106 and a plated conducting wire (also called a tie bar) 108. However, in the DIMM type circuit board technique, because a plating operation is often required after performing an etching operation to obtain independent copper conducting wires, conductive pathways must be pre-formed. For example, to plate the copper conducting wires of the gold finger bodies 106 in the gold finger 104 area, the specially retained tie bars 108 are used to receive the current from a cathode pole outside the board. In a subsequent cutting process to form the circuit board after the plating operation, the circuit board is cut along a board edge 110 to form the gold finger 104 leads as shown in FIG. 1B.
However, cutting is normally performed using a cutting tool such as a sawing knife. Therefore, in the process of forming the circuit board or testing the DIMM product, some of the tie bars may be broken or peeled off due to plugging and unplugging. Moreover, these defects may occur when the DIMM type circuit board is subsequently installed.
Therefore, the industry frequently adopts the following methods to improve the DIMM type circuit board without changing the number of DIMM type circuit board layers or circuit design.
One method is to change the material of the tie bars so as to enhance the peel strength between copper skin and resin. However, the actual defect rate of the tie bars shows that the improvement on the defects is minimal.
Another method is to improve the forming pathway of the circuit board and perform a fine repair. This method has strict rules regarding the useful life of the cutting tools for performing the fine repair. Yet, the improvement is not significant. According to statistics, the defect rate of the tie bars is normally around 0.5%˜1%. By applying the foregoing method, the defect rate drops slightly from 1% to about 0.7%˜0.8%.
More recently, another method is to provide the circuit board with tilted edge. The results of measurement show that the defect rate can be reduced to about 0.5% (about 5000 DPPM).
Regardless of whether to change the material, improve the forming pathway or provide tilted edges, the standard cutting method is still used. Therefore, the interface between the metal of the tie bars and the epoxy resin layer and the fiber resin layer of the circuit board can be easily damaged, thereby leading to a reduction of tear resistance.